In the packaging of materials in general it is important to establish a seal that is effective to prevent leakage. The reliability of the seal becomes extremely important when the materials to be packaged are either caustic or otherwise harmful. For example, in the packaging of hair preparations that include ammonia, it is extremely important that the package seal be effective to prevent the escape of ammonia content.
Another application wherein a tight seal is required is in the packaging of soda and other carbonated beverages. It is well known that if an effective seal is not established, the carbonating gases will escape from the beverage before it is completely used, thereby resulting in the soda becoming "flat".
A packaging system which is becoming quite popular for retaining a wide variety of materials employs an injection, or extrusion blow molded container, which either can be opaque, translucent or transparent, and an injection molded closure therefor. Injection and extrusion blow molded containers or bottles can be made from a variety of different plastics, with one preferred plastic being a polyvinyl chloride that is formulated for use in an injection or extrusion blow molding process, as is well known in the art. A threaded closure for such a bottle or container can be made of low density polyethylene, polypropylene or other similar plastic material.
One way of providing a seal for a threaded container is to employ a threaded cap with an internal liner therein. However, this introduces an additional element into the construction, and thereby introduces additional material and labor costs into the fabricating process. Moreover, in the event that the liner becomes deteriorated or otherwise worn, the sealing capabilities thereof can be adversely effected, thereby resulting in undesired leakage. Leakage also can occur due to undesired tolerance variations in the manufacturing process, resulting in gaps or spaces between the internal liner and the upper surface of the container or bottle. Moreover, leakage can occur when the internal pressure in the container causes the top to "dome", thereby forcing the internal liner out of sealing engagement with the upper surface of the bottle.
Another well known arrangement for attempting to establish a seal between a closure and bottle is to include a downwardly projecting rib or fin on the inner surface of the cap for resiliently engaging an upper surface or edge of the bottle finish, when the closure is tightened onto the finish. The seal affected by this arrangement generally is created by either line contact between the fin and the upper edge or wall of the bottle finish, or by minimal surface engagement between said members. The effectiveness of this type of seal is largely dependent upon maintaining close tolerances in the manufacturing process. In the event that there are irregularities in the finish, resulting, for example, from tool marks or "blow by" in the molding process, undesired gaps can be created between the sealing surfaces, thereby causing undesired leakage of the packaged material.